Thermoplastic polymers that are easily molded into a variety of shapes, sizes, and thicknesses are commonly used in virtually every category of consumer and industrial articles. Although their use has become ubiquitous, such polymers do present drawbacks that must be addressed. The increasing awareness of the dangers of fire and smoke associated with the use of plastics has led to legislation and standardization of plastics formulations with regard to flame retardancy.
Organohalogen compounds, antimony trioxide, and combinations thereof have been used as a flame retardant additive for plastic materials. However, such additives can generate a significant amount of smoke and toxic gases upon exposure to flame. As a result, attempts have been made to minimize their use in favor of less toxic alternatives.
More recently, the use of magnesium hydroxide particles or aluminum hydroxide particles as a safer alternative has become increasingly prevalent. Magnesium hydroxide provides excellent flame retardant properties, as well as smoke suppression, in a variety of plastics including wire and cable applications. Magnesium hydroxide is also a non-toxic, non-corrosive additive, and it is often incorporated into elastomeric and plastic compounds where a non-halogen solution to fire resistance and smoke suppression is preferred.
Magnesium hydroxide undergoes an endothermic decomposition beginning at about 330° C. according to Formula (I) below:HeatMg(OH)2→MgO+H2O  (I)The endothermic decomposition of Mg(OH)2, which occurs during combustion, is the flame retardant mechanism. The water released during combustion has the effect of diluting the combustible gases and acts as a barrier, preventing oxygen from supporting the flame. The smoke suppression properties of magnesium hydroxide are believed to be due to the dilution effect of the water vapor on the combustible gases or due to a char formation with the polymer.
Despite the advantages of magnesium hydroxide, its use can be problematic in certain applications. For instance, to obtain very high levels of flame retardant ability (e.g., UL 94 rating), flame retardant additives must be added in large amounts, such as greater than 60 percent by weight, which can adversely impact the physical characteristics of the polymeric resin and render it unsuitable for application such as wire and cable insulation.
Although existing magnesium hydroxide particulate compositions offer some measure of flame resistance and smoke suppression, there remains a need in the art for compositions that offer even greater levels of fire protection without sacrificing the beneficial physical properties of the polymeric resin to which the flame retardant composition is added.